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Why "# {String}" is a common idiom in Ruby

A Ruby dev I know asked about this; See my answer below ... Are there any other better reasons?

Why So Many Ruby Programmers Do

"#{string}"

but not

string

since the second form is simpler and more efficient?

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8 answers


Is this a common idiom for Ruby developers? I don't see that.



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Smaller changes where you later need to do more than just get the value of the string, but also add / add to it at the point of use, seems like the best motivation I can find for this idiom.



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There is only one case where this is the recommended idiom:

fname = 'john'
lname  = 'doe' 
name = "#{fname} #{lname}"

The above code is more efficient than:

name = fname + ' ' + lname

or

name = [fname, lname].join(' ')
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What is the broader context of some of the customs? The only other thing I can think of, beyond what has already been mentioned, is like trying to lose type safety; that is, you can take anything as an argument, and that can ensure that whatever you go for walks is like a duck ... or, well, a string (although string.to_s

it might be clearer though).

All in all, though it's probably a code smell that the person thought was "Best Practice".

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I use this type of code so I can pass nil

as a string and it will still work on the string and not see some exceptions:

def short(string = nil)
  "#{string}"[0..7]
end

And it's easier / faster to add debug code if it's already in quotes.

So, in short: it's more convenient.

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Maybe this is an easy way to convert any to string? Because it is the same as calling method to_s

. But this is pretty weird :).

a = [1,2,3]
"#{a}"
#=> "123"
a.to_s
#=> "123"
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Interesting answers, everyone. I am the developer who asked the original question. To give some context, I see this sometimes in my current work, and also sometimes in sample code in a Rails list with variables that are known in advance to contain strings. I could understand this as a replacement for to_s, but I don't think what's going on here; I think people just forget that you don't need the interpolation syntax if you are just passing in a string variable.

If anyone tried to tell me it was best practice, I would have escaped as quickly as possible.

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I could imagine this is useful in cases where the object being interpolated is not always a string, since the interpolation implicitly calls #to_s

:

"#{'bla'}"           => "bla"
"#{%r([a-z])}"       => "(?-mix:[a-z])"
"#{{:bla => :blub}}" => "blablub"

Might make sense when registering something where you don't care that much about the output format but never want an error due to the wrong argument type.

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